Pediatric-type diffuse low-grade gliomas with MYB alterations: Neuroimaging of the Diffuse astrocytomas,MYBorMYBL1-altered

Diffuse astrocytoma, MYB or MYBL1-altered is a new tumor type in the family of Pediatric-type diffuse low-grade gliomas and genetically related to angiocentric glioma. Imaging features of Diffuse astrocytoma, MYB or MYBL1-altered are less well known. During our clinical work, we identified a relatively characteristic imaging pattern in a subset of our patients consisting of a large, diffuse hemispheric tumor with displaced central vessels which we termed the "fireworks sign". Therefore, the purpose of this work was to describe the frequency of this sign and any additional imaging characteristics in a large patient cohort. This international retrospective study included 40 patients from 7 countries. We recorded clinical, genetic and standard radiological features focusing on the presence of the "fireworks sign" but also the presence or absence of a mismatch between T2WI and FLAIR and a FLAIR rim which have both been reported in these patients. Most tumors were unilateral and located in the cerebral hemispheres (most frequently in parietal, temporal and frontal lobes), hypointense on T1WI and hyperintense on T2WI. No tumor showed diffusion restriction. The "fireworks sign" was present in 16 patients. Other features included: T2/FLAIR mismatch (24 cases), FLAIR rim (18 cases), necrosis (5 cases) and enhancement (5 cases). Tumor volume was significantly associated with the "fireworks sign" (p=0.01) and T2/FLAIR mismatch (p=0.005). Imaging features of Diffuse astrocytoma, MYB1 or MYBL1-altered in children are variable and the "fireworks sign" was identified in a subset of patients only. It was usually present in patients with large hemispheric tumors but also observed in brainstem lesions. Diffusion restriction was consistently absent and enhancement infrequent. A T2/FLAIR mismatch was seen in more than 50% of patients. WHO = World Health Organization; DA-MYB = Diffuse astrocytoma, MYB or MYBL1-altered.